SALEM, Ore. – The persistence of both a detective and the victim’s sister has solved a murder in Oregon—38 years after it happened.

On March 9, 1979, Janie Landers disappeared outside the Fairview Training Center for the developmentally disabled where she lived in Salem, per the AP. Five days later, the 18-year-old’s body was discovered in a remote field, with deep stab wounds in her neck and her head bashed.

Witnesses had seen Janie, who functioned at about the level of an 8-year-old child, get into a stranger’s car. The police questioned several people, but all their leads turned into dead ends. As the years passed, Landers’ younger sister, Joyce Hooper, kept pushing the authorities to solve the crime.

In March 2015, the 36th anniversary of the murder, Hooper pushed again, and the state police reopened the case.

Detective Steve Hinkle and other investigators, examining photos of deep stab wounds near Janie’s neck, noticed that there were no abrasions from a weapon handle known as a hilt, and they concluded the killer’s hand probably slipped while he stabbed Landers, cutting himself and leaving his own DNA behind.

They retested blood on Landers’ shirt and found a DNA match to a man named Gerald Dunlap, who had worked in Fairview’s laundry in 1979.

The investigators learned that Dunlap had died behind bars in 2002, where he had been serving time on a separate rape conviction. “Final closure would have been seeing him convicted of her murder,” says Hooper. “But how I try to look at is: he died in prison. He wasn’t out there hurting anyone else.”